TreeWat is a tool designed to optimize a limited irrigation water supply in orchard crops. It provides an estimation of the relative decline in production of an orchard which receives insufficient irrigation water to meet its maximum crop water requirements (ETc), resulting in a reduction in its consumptive use. Furthermore, TreeWat provides optimal irrigation scheduling under irrigation supply restrictions, based on what is known of the specific tree responses to water deficits at different growth stages. Six different tree crops (almond, citrus, peach, pistachio, plum, olive) are considered in this first model version.

TreeWat computes all the water balance components of the orchard on a daily basis (runoff, deep percolation, change in root zone soil water content, evaporation from the soil, and tree transpiration) and obtains seasonal values for actual transpiration (Ta) and for maximum transpiration (Tp). Using an empirical function that relates seasonal transpiration to seasonal production in relative terms, the model calculates the expected relative yield reduction based on the relative transpiration reduction. These functions reflect the optimal responses observed with deficit irrigation that avoids severe stress at critical periods.

The model outputs are the full irrigation requirements (obtained when water supply is sufficient), the optimal irrigation schedule under water restrictions, and the corresponding decline in production predicted. Furthermore, all the water balance components associated with both, the full and deficit irrigation schedules are reported.